I18N: Add a new way to determine whether a translation is available.

A new `has_translation()` function can be used to determine whether a translation exists for a given string.

Props louiswol94, swissspidy, drzraf, ckanitz, tomhine, mchirag2002, samuelsilvapt.
Fixes #52696.


Built from https://develop.svn.wordpress.org/trunk@59029


git-svn-id: http://core.svn.wordpress.org/trunk@58425 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/l10n.php

@@ -1988,3 +1988,17 @@ function wp_get_word_count_type() {
 
 	return $wp_locale->get_word_count_type();
 }
+
+/**
+ * Returns a boolean to indicate whether a translation exists for a given string with optional text domain and locale.
+ *
+ * @since 6.7.0
+ *
+ * @param string  $singular   Singular translation to check.
+ * @param string  $textdomain Optional. Text domain. Default 'default'.
+ * @param ?string $locale     Optional. Locale. Default current locale.
+ * @return bool  True if the translation exists, false otherwise.
+ */
+function has_translation( string $singular, string $textdomain = 'default', ?string $locale = null ): bool {
+	return WP_Translation_Controller::get_instance()->has_translation( $singular, $textdomain, $locale );
+}